1. Field of the Invention
The present invention relates to a remote sensing method and a device, and more particularly, to a remote sensing method and a device utilizing microwaves to remotely measure waveforms directly related to electrocardiographic data, bioimpedance data, phonocardiographic data, and respiration pattern.
2. Description of Related Art
Information concerning a patient's respiration and heart function is vital to the diagnosis and monitoring of many medical conditions. An electrocardiograph is a device that is commonly used to provide information, often in the form of an electrocardiogram, concerning heart function. Electrocardiographs provide outputs that are indicative of electric fields created by the heart as it beats. Operation of an electrocardiograph typically requires attachment of nine leads, which are combined to obtain twelve sets of measurements. A large body of clinical experience has been amassed which has revealed correlations between specific shapes in the waveforms output by an electrocardiograph and many different types of heart conditions.
An impedance cardiograph is another device that is used to provide information, often in the form of an impedance cardiogram, concerning heart function. Impedance cardiographs measure changes in impedance within tissue to estimate changes in volume of a patient's body and organs. In several systems, alternating currents are transmitted through a patient's chest. The current seeks the path of least resistance, which theory predicts to be the blood filled aorta. As blood volume and velocity in the aorta change with each heartbeat, so too does the impedance of the tissue in the patient's chest. The changes in impedance can be used for diagnostic purposes.
Sounds made by the heart as it beats are the most commonly used indicator of basic heart function. A physician typically listens for the normal first, S1, and second, S2, heart sounds using a stethoscope pressed against the patient's chest. If sounds in addition to S1 and S2 are heard, such as a so-called “heart murmur,” these sounds indicate that further tests are necessary to assess the condition of the patient's heart. Such additional sounds should not normally be present, and can indicate a variety of abnormal heart conditions, such as a leaky heart valve, for example. A phonocardiograph is a device commonly used to provide detailed information on heart sounds, usually in the form of a phonocardiogram. The phonocardiogram waveform is measured by placing a sensitive microphone, or accelerometer, in contact with the chest at one of several well-defined auscultation locations. There is a large body of clinical data to assist in interpreting the phonocardiogram for diagnostic purposes, such as, for example, Rangaraj M. Rangayyan and Richard J. Lehner, “Phonocardiogram signal analysis”, CRC Critical Reviews in Biomedical Engineering, vol. 15, issue 3, pp. 211-236 (1998), which is herein incorporated by reference.
Electrocardiographs and impedance cardiographs typically involve attaching electrical leads to the subject being measured, and impedance cardiographs typically involve passing a current through the subject's body. Phonocardiographs require attaching a specially-designed microphone or accelerometer to the subject's torso.
U.S. Pat. Nos. 6,122,537; 5,760,687; 4,958,638; 6,753,780; 6,208,286; 6,031,482; and 5,488,501, which are herein incorporated by reference, demonstrate modulation of the phase and/or frequency of a reflected microwave signal (i.e., radar or Doppler radar techniques) to provide a measurement of pulse rate and/or respiration rate.